1. Field of the Invention
The invention in question concerns a device for illuminating components of transparent material so that the components may be tested for surface irregularities and occlusions.
Components of transparent material, for example optical or opthalmic lenses, must be tested for flaws prior to their utilization, particularly for surface flaws such as scratches, smears, cracks, chipping, stains, etc., and for occlusions such as bubbles or streaks. Such flaws would limit the usability of a lens if these were to exceed the limit values stated in DIN 3140.
Conventionally, the testing of optical components is carried out by personnel in the form of visual inspection. Such a test must be performed to a large extent in a darkened room. It is expensive, not sufficiently objective and, due to the high degree of monotony of the testing procedure, not sufficiently reliable.
2. Discussion of the Prior Art
Efforts have, therefore, been made to develop methods and devices for automatic, objective testing of optical components. From DE-OS No. 32 37 511, the method is known of placing optical components to be tested in the optical beam path of a television camera and of displaying through the component a test pattern on the camera. The disturbances caused by flaws in the component, produce a video signal which deviates from the control signal not influenced by the component. The flaw is deduced on the basis of the deviation between the control and actual signal. A device acting on this principle is rather expensive and is not able to detect smaller flaws, for example, those resulting from scratches, smears or hair-line cracks.
In order to increase the sensitivity of the testing procedure, it is recommended in DE-OS No. 30 11 014 that the component to be tested be illuminated completely, a television image be produced, and the video signal be analyzed line for line. This method is also complicated, expensive and not sufficiently exact.
An even older recommendation for a test method is to be found in DE-OS No. 23 37 597. According to this, a light ray is focused on the surface of the component to be tested and is punctiformly moved over the surface, at the same time being kept in focus. The light penetrating the component is reflected backwards, passes through the component again, and then falls onto a detector. Deviations in the intensity of the receiver signal make it possible to deduce a flaw and also to localize this.
A device acting on this principle is very expensive. It only allows that surface of the work-piece to be tested onto which the scanner ray is focused. Illumination of the object to be tested is, in this case, achieved in that the test piece rotates on its axis and the impinging light ray is slowly radially deflected in such a way that it describes a spiral-type pattern on the test piece, whereby its state of focus must be continuously readjusted according to the curvature of the surface to be scanned.